Project Summary: The goal of the study is to contribute to reductions in HIV incidence among youth in sub- Saharan Africa. Our objective is to advance that goal by evaluating the efficacy of an interactive smartphone game that is designed to prevent HIV among African adolescents by delaying sexual debut and increasing condom use at first sex. The game-based intervention has shown promise in an NIMH-funded randomized feasibility study in Kenya. The intervention is informed by socio-behavioral and pedagogical theories, evidence- based practice, and unique formative research on youth sexual culture in sub-Saharan Africa. Tumaini (meaning ?hope for the future? in Kiswahili) is a choose-your-own-adventure game app for inexpensive Android smartphones that uses interactive narrative to promote observational learning, cognitive and behavioral rehearsal, problem-solving, and immersion. Tumaini is designed to increase age and condom use at first sex by: increasing knowledge about sexual health and HIV; building risk-avoidance and risk-reduction skills and related self-efficacy; challenging HIV stigma and harmful gender norms and attitudes; fostering future orientation, goal- setting, and planning; and promoting dialogue with adult mentors. The game follows six characters (3 girls, 3 boys) with diverse socio-demographics and backstories, as they proceed through adolescence over three game levels. Players make decisions for the characters and experience the consequences of those decisions on characters' lives, health, and future goals. The study will follow a gender-balanced sample of 912 Kenyan adolescents, aged 13-14 at enrolment, and randomly assigned to the intervention or to a control game for 45 months with 4-monthly behavioral assessments. It will test for HIV and HSV-2 at baseline and endline, analyze game log files from the phones of intervention arm participants, and conduct qualitative research with participants, their parents and other stakeholders. The proposed project has the following aims: (1) Determine if a theory-based, empirically grounded mobile phone game-based intervention delays sexual debut and increases condom use at first sex; (2) Determine whether the game-based intervention influences behavioral mediators (knowledge, attitudes, behavioral intentions, and related self-efficacy) of early and unprotected sex; (3) Through analysis of outcome data and the mobile phone log files, determine which game components and theoretical constructs mediated effects. In addition, we have the following secondary aims: (SA1) Determine whether the game reduces HSV-2 and HIV infection; (SA2) Conduct qualitative research to optimize trial implementation, monitor threats to internal or external validity, strengthen the intervention's theory of change, and inform potential dissemination. If proven efficacious, the proposed intervention has the potential to be highly scalable, low cost, and culturally adaptable to individual sub-Saharan countries.